1. Field of the Invention
The present invention relates to a toner replenishing apparatus utilizing an electrophotographic system such as copiers, facsimile machines or printers, and an image forming apparatus equipped with the toner replenishing apparatus, and more specifically, relates to a toner replenishing apparatus capable of recovering toner residue on a photoconductor for reuse in development of an electrostatic latent image to provide a stable image, and to an image forming apparatus equipped with the toner replenishing apparatus.
2. Description of the Related Art
Hitherto an image forming apparatus utilizing a electrophotographic system such as copiers, facsimile machines or printers performs image formation by adhering toner to an electrostatic latent image formed on a photoconductor by developing means to make the image visible, transferring a toner image formed by thus making the image visible to a material subject to transfer such as a sheet of transfer paper and fixing the visible image. In such a process of image forming, while most of the toner adheres to the electrostatic latent image on the photoconductor in transferring to a sheet of transfer paper or the like, part thereof remains on the photoconductor without transferred and is recovered by cleaning means serving as recovering means.
This toner residue on the photoconductor is easy to be adversely affected by environmental conditions. For instance, under conditions of high temperature and high humidity, reduction in transfer efficiency is caused and toner residue on the photoconductor increases. Moreover, a minute amount of toner adhering to the photoconductor in a region where the electrostatic latent image is not formed and remaining on the photoconductor without being transferred is also recovered by the cleaning means. In addition, a visible image of a reference density pattern formed on the photoconductor for the purpose of process control such as control of toner concentration also remains on the photoconductor without being transferred and is recovered by the cleaning means.
On the other hand, in connection with recent environmental problems, it is natural that effective use of resources is increasingly valued even in OA appliances. As for use of toner in image forming apparatuses utilizing the electrophotographic process, it is usual that in the conventional image forming apparatus, about 20% of toner to be used is recovered by the cleaning means without being transferred to a sheet of transfer paper to become waste toner, and discarded as industrial wastes.
In view of the above, such an image forming apparatus as follows is proposed. In order to effectively reuse toner recovered by the cleaning means (referred to as recovery toner hereinafter) by using a toner recycling mechanism, the image forming apparatus is configured so as to convey and replenish recovery toner in the cleaning means to the side of the developing means and reuse the toner as recycled toner, thereby increasing the available volume of image formation as well as eliminating a drudgery of discarding waste toner of the image forming apparatus to reduce inconvenience for the user.
In Japanese Unexamined Utility Model Publication JP-U 59-166264 (1984), it is enabled that from the outlet of a cleaning apparatus for removing toner residue on a photoconductor after transfer, removed toner which is recovery toner is conveyed to a toner replenishing section to which new toner is also conveyed, and thereby the removed toner and the new toner are mixed and replenished to a developer.
Next, in Japanese Unexamined Patent Publication JP-A 9-236978 (1997), although old toner which is recovery toner and new toner are mixed and replenished to a developer as well as in JP-U 59-166264 mentioned above, a method for mixing the old and new toners is notable. That is to say, attention is directed to a problem such that due to toner with unstable characteristics which is generated in the case of recycling toner to repeatedly develop electrostatic latent images, the developed images become unstable and a fog in a white region exceeds a permissible value. Therefore, it is enabled that when the old toner and the new toner are mixed, the mixture ratio between the old and new toners is controlled by a CPU, and as the volume of image formation increases, the ratio of the old toner is reduced.
Next, in Japanese Unexamined Patent Publication JP-A 6-110329 (1994), in order to limit the convey amount in a convey path for conveying recovery toner to the toner replenishing section and the convey amount of toner supplied from the toner replenishing section to the developer, into a given range, the convey amount in the convey path is controlled, a toner replenishing roller is controlled with respect to the developer, a toner temporary container is placed in a recovery toner convey path, a shutter is placed at the outlet of the recovery toner convey path, a container of the recovery toner is placed, and so on. Moreover, it is also enabled that the ratio between the new toner and the recovery toner is regulated based on the concentration of the old toner and the replenishing amounts of the respective toners are controlled based on the developing ability and the result of detecting the density of a reference image for detecting failed toner.
With regard to JP-U 59-166264, there is a problem such that when toner is continuously recycled by the toner recycling mechanism to form images, image density gradually declines during a period of time when the same toner is used. Further, in connection with the declination of image density, there is a problem such that fogs in a white region gradually increases during the period of time when the same toner is used. Furthermore, there is a problem such that as the amount of recycled toner increases in the same toner, the amount of scattered toner increases around a photoconductor. In addition, the recovery toner to be reused deteriorates after undergoing the process of image forming many times to be hardly charged with electricity as a result or to come to contain toner which is charged to the opposite polarity, with the result that the replenishing amount of the recovery toner decreases with time. As a result, such a problem is caused that the amount of the recovery toner in the recovery toner container continuously increases with time, the recovery toner container is filled with the recovery toner in a short time, the recovery toner floods, and the recovery toner agglomerates due to increase of the pressure inside the recovery toner container, with the result that images are chipped because of a failure of supplying the recovery toner and use of a mass of recovery toner in development. Further, there is a problem such that a fog caused by charge-failed toner results in deterioration of the image quality such as a stain. In this case, the fog means that toner transfers to a non-image region in which there is no electrostatic latent image.
In JP-A 9-236978, in order to solve the aforementioned problems, it is enabled that the mixture ratio between the old and new toners is controlled by a CPU, and as the volume of image formation increases, the ratio of the old toner is reduced. However, it is impossible to implement an apparatus at a low cost because a control function by the CPU is necessary in this method, and the overflow of an old toner hopper is not taken into consideration.
Further, in JP-A 6-110329, the mixture ratio between the toners is regulated by controlling the convey amount of the convey path, controlling the toner replenishing roller with respect to the developer, placing the recovery toner container in the recovery toner convey path, placing the shutter at the outlet of the recovery toner convey path, placing the recovery toner container, and the like, so that it is impossible to implement an apparatus at a low cost, and the overflow of a recovery toner container is not taken into consideration.